The Exponential Growth of Cells
I am sure most of you know that cells are the basic unit of life. They are all around us, from the blood cells that make up our bodies to bacteria on a door handle, they are found almost everywhere on our planet unless the area is sterile. Without cells, life could not exist.
I am currently researching an emerging field called cellular agriculture, which involves culturing an animal’s stem cells to produce products identical to the real thing. With this in mind, I was curious as to how one tiny cell could grow into something that could feed an entire family.
There are many rules and regulations around access to labs and stem cells during these times. Labs are closed so most experiments have to be done at home. This didn’t stop me from pursuing a similar experiment so I turned to the most common cell — bacteria.
I knew that I wanted to grow bacteria cells but how might one do that? Sure, they naturally grow around us, but I wanted to get visible results in a relatively short amount of time. The secret to this: agar.
- agar - a jelly like substance obtained from various kinds of red seaweed, often used in biological culture media.
Agar is the most preferred bacteriological culture media because it is an inert substance, providing a solid growth surface for the bacteria, upon which bacteria reproduce until the distinctive lumps of cells that are called colonies form.
Preparation Of Agar Plates
A Petri dish is a shallow, circular, transparent dish with a flat lid, used to culture microorganisms. They will contain the agar and bacteria in a safe environment to grow.
It is essetial that all of the equipment being used in this process has been sterilized. Contamination or other disruptance could be catastrophic to the experiment. To sterilze the equipment I put them in boiling water for 20 minutes.
To prepare the agar plates, first, I measured the agar, using ratios given proportionate to 250mL of water
- For the Nutrient Agar, a ratio of about 5.3g/mL
- For the Potato Dextrose Agar (PDA), a ratio of 10g/mL
- For the Malt Extract Agar (MEA), a ratio of 14g/250mL
After that, I brought the total of 750mL of water to a boil and combined 250mL with each bowl, stirring until dissolved.
Normally, the next step would be to use an autoclave - a machine that uses steam heat to kill any microbial life that may be present. Since I didn't have access to one, I used my microwave instead.
Lastly, I poured the agar solutions into the Perti dishes, filling the bottom up from 1/2 to 2/3 full, then I tilted it to get an even distribution. Then I let it cool for an hour and 30 minutes to allow it to cool down into its jelly-like form.
Bacteria Time!
For starters, you should know that bacteria grown in a lab environment is referred to as a culture.
- Pure culture: contains only one type of bacteria
- Mixed culture: contains more than one type of bacteria
For this experiment, I will be using a mixed culture as they tend to have a higher growth rate and product yield, key to analyzing the results. I wanted a relatively consistent source of bacteria so I swabbed the inside of my cheek(as gross as it sounds, it is justified in the name of science!)
After that, I gently streaked the surface of the prepared agar plates as to not cause any tears while getting a good distribution of the bacteria. Each dish was labelled with a name according to the type of agar used and number to indicate where they would be stored.
Setting Up The Environments
Cells need the right conditions to grow. In addition to testing different nutrients with different agar, I wanted to test how temperature would affect a cell’s growth. For cellular agriculture, the environment of the culturing should be as close to the animal.
Since the original source of bacteria I got was from myself, I tested the three solutions at the average body temperature of 37°C. This was the most challenging environment to set up as finding a way to heat up, and keep at a consistent high temperature involved a DIY solution.
For starters, a source of heat. I found lightbulbs to be the best as they don’t use too much energy, are relatively safe to leave on for a few days, and easy. After that, I needed a way to heat the Petri dish without overheating it. Using 2 sizes of empty and sterile yogurt containers, I stacked the larger one on top of the smaller, creating a closed, raised platform for the dish to sit on. I cut a slit in the bottom section and used duct tape to seal the two containers. In addition, I added tinfoil to insulate and redirect escaping heat. It was very tedious but I slowly made adjustments until I got the right temperature.
Then I thought it would be interesting to see how the samples would grow in the normal room temperature of my house that I’ve been locked up in during Covid. This could mimic a lab-like environment without heating devices. If this works it would save on costs and be easier to implement.
And finally, I wanted to see how the bacteria would handle in harsher conditions by putting one set of the petri dishes in the fridge (4°C), just as if the power went out during a cool winter.
Results
What I found was quite interesting to say the least.
Out of the 9 Petri dishes, only 2 exhibited visible bacteria colonies — both in nutrient media — one at room temperature and one at 37°C. I believe that the bacteria in the three dishes stored in the fridge died off due to the cold temperature.
I believe my results were due to both the type of bacteria I collected and the conditions it was grown in. Considering that the bacteria grew in the nutrient agar and not the PDA and MEA, I can assume that the PDA and MEA did not provide the appropriate nutrients required. The nutrient agar provided enough nutrients for the bacteria to grow. The room temperature and body temperature were also conducive to the growth. Too extreme on one of the side would disrupt the cells’ growth.
- Nutrient 1 - grew over a large area, visible condensation, most bacteria
- Nutrient 2 - more concentrated, smaller area
In conclusion, nutrient agar is the most versatile out of the 3. If this could be replicated in a field such as cellular agriculture, many of the major hurdles would disappear. Finding this “super-media” isn’t even confirmed to be possible but it’s definitely worth a shot so that one day, I can grow my dinner at home, instead of just bacteria.
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